concat_dataset.py

import bisect
import numpy as np
from torch.utils.data.dataset import ConcatDataset as _ConcatDataset


class ConcatDataset(_ConcatDataset):
    """
    Same as torch.utils.data.dataset.ConcatDataset, but 
    concat the group flag for image aspect ratio.
    """
    def __init__(self, datasets):
        """
        flag: Images with aspect ratio greater than 1 will be set as group 1,
              otherwise group 0.
        """
        super(ConcatDataset, self).__init__(datasets)        
        if hasattr(datasets[0], 'flag'):
            flags = []
            for i in range(0, len(datasets)):
                flags.append(datasets[i].flag)
            self.flag = np.concatenate(flags)

    def get_idxs(self, idx):
        dataset_idx = bisect.bisect_right(self.cumulative_sizes, idx)
        if dataset_idx == 0:
            sample_idx = idx
        else:
            sample_idx = idx - self.cumulative_sizes[dataset_idx - 1]
        return dataset_idx, sample_idx